Threshold parameters for choroidal vessel closure with the photosensitizer, lambda 27.

Objective: To determine the threshold photodynamic therapy parameters, required for choroidal vessel closure, with the photosensitizer, Lambda 27, in Dutch belted rabbits, using fluorescein angiography and histopathology.

Design: A pre-clinical experiment.

Place And Duration Of Study: Department of Ophthalmology at the Tulane University Health Sciences Center, between June 2001 - July 2002.

Patients And Methods: Dutch belted rabbits were divided into two groups. The first group was injected intravenously with an aqueous solution of Lambda 27 at 1mg/kg. Saline was injected intravenously into the second group (controls). Approximately 5 minutes after injection of Lambda 27, a diode laser, mounted on Zeiss 30 SL-M slit lamp, emitting light at a wavelength of 719 nm was used to apply photodynamic therapy to the fundus. Lesions were placed on the choroid of the rabbits at a fixed spot size of 1.5 mm, using powers ranging from 50 to 120 mW, for a duration of 5 to 80 seconds. Choroidal vessel closure was documented by fluorescein angiography, the following day, and by light microscopy, after the animals were sacrificed.

Results: Choroidal vessel closure was documented using fluorescein angiography for all of the lesions placed at fluence of 22.7 J/cm2 and above. Histopathology also confirmed this finding. No choroidal vessel closure was seen in the rabbits treated with fluences less than 22.7 J/cm2 or in the control group.

Conclusion: This experiment establishes threshold parameters for choroidal vessel closure using the photosensitizer, Lambda 27.